Every Case Calendar calendar publishes an .ics URL — the universal iCalendar subscription format (RFC 5545). Once that URL is reachable on the public web (see the public index page for one Caddy template), any modern calendar app can subscribe to it and pull updates on its own schedule.

This page collects each major app’s official subscribe-by-URL flow. The URL you’ll paste is whatever your deployment serves the .ics from — e.g. https://calendars.example.com/cybercrime.ics.

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A note on refresh frequency

Subscribed feeds refresh on the receiving calendar app’s own schedule — not on yours, and not when the underlying .ics file changes. The numbers vary by app and most aren’t configurable. Best published intervals at the time of writing:

App Refresh interval
Apple Calendar (macOS / iOS) User-configurable: 5 min, 15 min, hourly, daily, weekly, or manual
Google Calendar Not documented; typically every several hours, no user setting
Outlook on the web / Outlook.com “Approximately every 3 hours”; can take up to 24h
Proton Calendar Every 4–16 hours
Fastmail Hourly
Thunderbird User-configurable per calendar; default 30 min

If a hearing date moves and you can’t wait for the next refresh, most apps let you remove and re-add the subscription to force an immediate fetch. For zero-lag updates on the same events, see the Google Calendar / Microsoft 365 push backends, which write events directly rather than waiting for the subscriber’s pull.

Apple Calendar — macOS

Per Apple’s macOS Calendar User Guide:

  1. Open the Calendar app.
  2. Choose File → New Calendar Subscription.
  3. Paste the .ics URL and click Subscribe.
  4. Pick a name and color.
  5. For Location, choose iCloud to sync the subscription to every device on your Apple Account, or On My Mac to keep it local to this machine.
  6. Set Auto-refresh (5 min, 15 min, hourly, daily, weekly, or never).
  7. Click OK.

Subscribed calendars are read-only — events come from the publisher.

Apple Calendar — iPhone / iPad

Per Apple’s iCloud calendar subscription guide (steps differ slightly between iOS 26+ and iOS 18 or earlier):

iOS / iPadOS 26 or later:

  1. Open the Calendar app.
  2. Tap Calendars at the bottom of the screen.
  3. Tap Add Calendar → Add Subscription Calendar.
  4. Paste the .ics URL and tap Find.
  5. Give it a name and color.
  6. Next to Account, choose iCloud (so the subscription syncs to all your Apple devices), then tap Done.

iOS / iPadOS 18 or earlier:

  1. Open the Calendar app.
  2. Tap Calendars at the bottom.
  3. Tap Add Calendar → Add Subscription Calendar.
  4. Paste the URL and tap Subscribe.
  5. Name it and choose a color, then under Account pick iCloud and tap Add.

Older iOS releases also expose the same flow under Settings → Calendar → Accounts → Add Account → Other → Add Subscribed Calendar.

Google Calendar — web

Per Google’s “Add other calendars” help page:

  1. Open Google Calendar on a computer web browser (Google does not support adding a URL subscription from the Android or iOS Google Calendar apps).
  2. On the left, under Other calendars, click the + button.
  3. Choose From URL.
  4. Paste the .ics URL and click Add calendar.

Shortcut: the Add by URL form is also reachable directly at calendar.google.com/calendar/u/0/r/settings/addbyurl — skip the sidebar entirely.

The new calendar appears under Other calendars. It is read-only and syncs to every device signed in to the same Google account once it is added on the web. Google does not publish a refresh interval and there is no manual-refresh button — pulls happen on Google’s own schedule, typically every several hours.

Microsoft Outlook — Outlook.com, Outlook on the web, and the new Outlook for Windows

Per Microsoft’s “Import or subscribe” help page:

  1. Open Outlook on the web (or the new Outlook for Windows) and go to Calendar.
  2. In the left sidebar, click Add calendar.
  3. Choose Subscribe from web.
  4. Paste the .ics URL.
  5. Click Import.

Microsoft notes that “whenever events change on an iCal, it can take more than 24 hours for Outlook on the web to update your calendar,” with typical updates “approximately every 3 hours.” If the subscription fails, paste the URL into a browser tab first to confirm it serves an .ics file — most subscription failures are an unreachable or mistyped URL.

Proton Calendar

Per Proton’s “Subscribe to an external calendar” help page:

  1. Sign in at calendar.proton.me (or open the desktop / mobile Proton Calendar app).
  2. Open Settings → All settings → Calendars → Other calendars.
  3. Click Add calendar from URL.
  4. Paste the .ics URL and confirm.

Proton refreshes external subscriptions every 4–16 hours. A subscribed external calendar counts toward your plan’s overall calendar quota and is read-only (no editing, sharing, or export).

Fastmail

Per Fastmail’s calendar synchronization help:

  1. Sign in to Fastmail on the web.
  2. Open Settings → Calendars.
  3. Scroll to the Subscriptions section.
  4. Paste the .ics URL into the text box and click Subscribe to calendar.
  5. On the next screen, set a name and color, then click Save.

Fastmail polls subscribed feeds hourly.

Mozilla Thunderbird

Per Mozilla’s “Creating new calendars” help page:

  1. In Thunderbird’s calendar pane, open File → New → Calendar… (or click the ≡ menu → New → Calendar…, or right-click in the calendar list).
  2. Choose On the Network and click Next.
  3. Leave the username field empty (Case Calendar feeds are public — no credentials required). If the dialog has a “This location doesn’t require credentials” checkbox, tick it.
  4. Paste the .ics URL into the Location field.
  5. Click Find Calendars, pick the calendar from the result list, and click Subscribe.

Thunderbird’s per-calendar properties dialog lets you set the refresh interval (default 30 minutes).

Verifying the URL

Across every app, the first thing to check when a subscription fails is whether the URL actually serves .ics content. Paste it into a browser address bar:

If the server returns text/plain instead of text/calendar, desktop calendar apps may still subscribe but some mobile apps won’t — see the public index page Caddy template for the correct MIME type.

Next steps